Process for the conversion of acrolein and methacrolein to the corresponding unsaturated acids



United States Patent PROCESS FOR THE CONVERSION OF ACROLEIN AND METHACROLEIN TO THE CORRESPOND- ING UNSATURATED ACIDS James D. Idol, Jr., Shaker Heights, James L. Callahan,

No Drawing. Application December 17, 1957 Serial No. 703,269

9 Claims. (Cl. 260-530) This invention relates to the oxidation of unsaturated aldehydes. It deals with a new method of carrying out such an oxidation selectively to produce the corresponding unsaturated carboxylic acid in high yields. Another aspect of the invention deals with the use of certain catalysts for the conversion of unsaturated aldehydes to the corresponding unsaturated acids. The invention has particular utility in connection with the production of acrylic and methacrylic acids which may be subsequently converted to lower alkyl esters for use in the plastics industry.

The oxidation of saturated aldehydes to the corresponding saturated carboxylic acids is a well-known reaction which is carried out commercially on a large scale, especially for the production of acetic acid. Unsaturated aldehydes, however, have a marked tendency to underand silver vanadate.

go side reactions during oxidation, and consequently only poor yields of desirable acids are obtained under the usual conditions of reaction.

Some unsaturated acid can be obtained by oxidizing unsaturated aldehydes with hydrogen peroxide according to US. Patent 2,377,584 but large amounts of dihydroxy aldehyde are simultaneously producedin the patented process.

U.S. Patents 2,744,928 and 2,744,929 disclose methods by which unsaturated aldehydes may be converted to the corresponding unsaturated carboxylic acid. These methods involve a liquid phase reaction in the presence of a solvent and they require the use of both a catalyst and a peroxidizing agent such as hydrogen peroxide. This process has the disadvantage of involving solvent recovery oxygen is not as economic as other oxygen sources.

It is the object of the present invention to overcome the disadvantages of prior methods of producing unsaturated carboxylic acids from unsaturated aldehydes by providing an efiicient, commercially attractive method for converting unsaturated aldehydes to the corresponding carboxylic acids by direct vapor phase reaction of the aldehyde with oxygen in the presence of a catalyst. It has been found that unsaturated aldehydes can be selectively oxidized at the aldehyde group to produce high yields of unsaturated carboxylic acid by carrying out a catalytic vapor phase reaction employing oxygen as the oxidizing agent. It was most unexpected to find that an unsaturated aldehyde could be successfully oxidized to the corresponding unsaturated acid in the vapor phase in view of the known highly reactive nature of the double bond in unsaturated aldehydes both with reference to oxidation and polymerization. Workers in the prior art apparently believed that the reaction had to be carried out in the liquid phase and that if the reaction were conducted at the elevated temperatures necessary to a vapor phase reaction that useless side reactions of the unsaturated aldehydes would predominate over the desired reaction. However, we have discovered a process which surprisingly produces good yields of the unsatu- I 2,881,214 Patented Apr. 7, 1959.

rated acids. It was even more surprising that the undesirable side reactions which were thought to be characteristic of the unsaturated aldehydes do not occur to any appreciable extent in the process of our invention.

The unsaturated acids produced according to the process of this invention have wide utility in the plastics industry, either in their free form or as related compounds such as the esters. The ethyl and methyl esters of acrylic and methacrylic acids, for example, are in great demand at the present time.

In brief, the process of this invention is carried out by reacting an unsaturated aldehyde with oxygen in the vapor phase in the presence of a catalyst. The catalyst employed in this process may be selected from the group consisting of the oxides of vanadium, the oxides of silver, and silver vanadate. Another feature of the process relates to the addition of water in the vapor phase to the reaction zone, but the process is not limited to one in which water is added to the reaction mixture as the desired reaction will occur in the absence of water with some reduction in yield. The process of this invention is particularly applicable to the oxidation of aliphatic unsaturated aldehydes, e.g., acrolein and methacrolein.

As stated above, the catalytic agent employed in the process of this invention is selected from the group consisting of the oxides of vanadium, the oxides of silver,

In certain instances it may be desirable, to employ various combinations of the members of this group as the catalytic agent. Although the catalysts described herein may be employed in an unsupported form, we prefer to employ them in conjunction with a support. If a support is employed, the final catalyst should comprise at least 10 weight percent of the catalytic material and particularly good results are obtained when the final composition comprises at least about 20 weight percent of the catalytic agent. The preferred support is silica but it is not required that the silica be pure and it may contain small amounts of alumina. Other inert supports such as titania, zirconium oxide and the like may also be conveniently employed.

It is preferred that the surface area of the catalyst not be too great. It has been observed that a catalyst having a high surface area has a high activity which impairs the selectivity of the catalyst and it may result in the oxidation of the unsaturated aldehyde beyond the de- 'r de r e. rfa steps and the use of hydrogen peroxide as a source of $1 ed g e The Sn Ce area as measured by conven tional methods should be in the range of 1 to 250 square meters per gram and it is preferred that the surface area of the catalyst be in the range of about 25 to about 100 square meters per gram.

The catalytic agent may be incorporated on the support by means of either impregnation or co-gelation;

' treatment- Oxygen for the process of this invention may be supplied either in the form of air or as free molecular oxygen and the reaction will proceed to some extent in the absence of added oxygen since the catalyst employed in I the process will furnish some oxygen to the reaction, but

The amount of oxygen'fed to the reactor based on 1 mol 'of unsaturated aldehyde should be in the range of 0.5 to 50 mols, but the best results are obtained when the molal ratio of oxygen to unsaturated aldehyde is about 1:1.

As mentioned heretofore, water has a beneficial effect on the course of the reaction and relatively large quantities of water may be fed to the reactor along with the unsaturated aldehyde. The molal ratio of water to the unsaturated aldehyde may be in the range of :1 to 12:1, but a ratio of about 3:1 is preferred.

The temperature at which the reaction is to be conducted has an effect on conversion; and while temperatures in the range of 400 to 850 F. may be employed, the best results are obtained when the temperature is in the range of about 450 to 600 F. A temperature of about 475 F. appears to be optimum for the conversion of acrolein to acrylic acid. Generally, the reaction is carried out at about atmospheric pressure but other pressures are also operable.

Another process variable is the apparent contact time which is defined here below:

Apparent contact time Apparent volume of the catalyst in the reactor The volume 'of ma't'erial fed to the reaction is measured at the conditions of the reaction. In connection with the present process, it is customary to describe the-contact time in terms of seconds. Bro'adlysta'ted, contact times of -1 to 150 seconds have been'found to be operable, but the preferred range is 15 to 25 seconds.

The process of this invention may be conducted intermittently or continuously. A fixed-bed reactor employing a pelleted form of a catalyst may be employed, and it is also feasible to conduct the process in a reactor containing a fluidized catalyst bed. Since the reaction is exothermic, the temperature within the reactor must be regulated in order to control the reaction. It appears that the operation of a fluidized bed reactor offers some advantage from the standpoint of temperature regulation within the reactor.

The catalyst employed in this process is not materially afiected by the reaction, and since 'it'is not usually necessary to regenerate the catalyst -no provision is ordinarily made for regeneration. However, catalyst regeneration is contemplated within the scope of this invention as certain operations may require such "a step.

The products of this re'actionmay include carbon monoxide, carbon dioxide, and the unsaturated acid together with any unconverted unsaturated aldehyde. The desired product of the reaction; namely the unsaturated acid, may be recovered from the reactor efiluent gases by conventional methods such as "condensation, scrubbing with water or other suitable solvent, or compression followed by a subsequent expansion. If water scrubbing is employed in the case of the low molecular weight acids, it is advantageous to employ a hot scrubbing solution since the unreacted aldehydes and other light gases will generally boil at lower temperatures than the acids and they may be purified and recycled directly to the reactor. If there are any difficulties due to polymerization of the unsaturated acid when the product is recovered by'water scrubbing, such difficulties may be overcome by adding a small amount of any of the known polymerization inhibitors to the scrubbing solution; as for example, hydroquinone. Other additives may also be conveniently employed, but inhibitors containing an amine should be avoided as they tend to accelerate polymerization.

In order to more fully illustrate the process of this invention, a number of illustrative examples of the proc- 4 ess are given below. In the examples the following definitions are employed:

Conversion Weight of unsaturated aldehyde in the feed Weight of unsaturated aldehyde in the efiluent Weight of unsaturated aldehyde in the feed Weight of unsaturated aldehyde in the feed Weight of unsaturated aldehyde in the efiiuent In the case where acrolein is the unsaturated aldehyde to be oxidized, the amount of acrolein is determined by treating an aliquot of'a solution with excess dinitrophenyl hydrazine or by vapor phase chromatography. Acrylic acid which is the product of the acrolein reaction was determined by titrating an aliquot of an aqueous solution with sodium hydroxide. The titrated solution was evaporated to dryness and the salt recovered therefrom was analyzed by infra-red for the acrylate. In all of the examples given below the products of the reaction were recovered by scrubbing the efiluent gases from the reactor with cold water. The resulting solution is referred to in connection with the analyses mentioned above.

The examples which follow illustrate the advantagw of our invention. All of these runs were made at atmospheric pressure.

Example! A silver vanadate catalyst was prepared in the following manner:

12.9 g. of ammonium vanadate was dissolved in 7.00 ml. of water with 18 g. of oxalic acid. This solution was mixed with 134 g. of a 30% aqueous solution of low alkali colloidal silica. Next, 18.7 g. of silver nitrate was added to the mixture and the final mixture was gelled by adding ammonium hydroxide. The gel was oven dried at 300 F. and then heated in air for 2 hours at 1000 F. The final product was ground to a +40-100 mesh size.

30 g. of the catalyst were placed into a conventional oxidation reactior. A gaseous mixture having the following composition was then fed to the reactor:

Ingredient: Volume percent Acrolein 20 Oxygen 20 Water 60 At a temperature of 430 F. and a contact time of 19 seconds the total conversion was 8.6% and the yield of acrylic acid was 43%.

In another run employing the same catalyst, a gaseous mixture having the following composition was fed to the reactor:

Ingredient: Volume percent Acrolein Oxygen Water 70 At a temperature of 570 F. and a contact time of 19 seconds the total conversion was 12.4% and the yield of acrylic acid was 26.4%.

In still another run on this same catalyst, a gaseous mixture having the following composition was fed to the reactor:

Ingredient: Volume percent Acrolein -c. 33 Oxygen 67 At a temperature of 420 F. the total conversion was 19.4% and the yield of acrylic acid was 0.7%. This run clearly demonstrates the beneficial effect resulting from the presence of water in the reaction mixture. It is noted that in a comparable run containing 60% water, the yield Qf acrylic acid was 43%.

.5 Example II A silver vanadate-vanadium oxide catalyst was prepared in the following manner:

A solution containing 200 ml. of a solution containing 30 g. of ammonium vanadate and 45 g. of oxalic acid was added to 270 g. of a 30% aqueous solution of low alkali colloidal silica. A solution of 19 /2 g. of silver nitrate in water was added to this mixture. The mixture was flash dried and heated in an oven at 150 C. for 12 hours and then calcined at 1000 F. for 2 hours.

80 g. of the catalyst were ground and screened to 40- 100 mesh. 30 g. of this catalyst were placed in a conventional oxidation reactor and a gaseous feed having the following composition was reacted therein:

Ingredient: Volume percent Acrolein 20 Oxygen 20 Water 60 Ingredient: Volume percent Acrolein 16 Oxygen 33 Water 49 At a temperature of 500 F. and a contact time of 19 seconds the total conversion was 23.2% and the yield of acrylic acid was 15.2%.

Example III A silver vanadate-silver oxide catalyst was prepared according to the following procedure:

200 ml. of a solution containing 30 g. of ammonium vanadate and 45 g. of oxalic acid was added to 270 g. of a 30% aqueous solution of low alkali colloidal silica. A water solution of 78 g. of silver nitrate was then added to this mixture. The mixture was flash dried and then placed in an oven at 150 C. for 12 hours and calcined at 1000 F. for 2 hours. The catalyst was ground and screened to 40-100 mesh.

30 g. of this catalyst were placed in a conventional oxidation reactor and a gaseous feed having the following composition was reacted therein:

Ingredient: Volume percent Acrolein 20 Oxygen 20 Water 60 all modifications of the invention which would reasonably fall within the scope of the appended claims.

We claim:

1. A process for the manufacture of an a, 9-unsaturated mono-carboxylic acid which comprises the step of reacting an a,/3-unsaturated aldehyde selected from the group consisting of acrolein and methacrolein with oxygen in the vapor phase at a temperature in the range from about 400 F. to 850 F. and in the presence of a catalyst comprising at least one member of the group consisting of the oxides of vanadium, the oxides of silver, and silver vanadate.

2. A process for the manufacture of an a,B-unsaturated mono-carboxylic acid which comprises the step of reacting an cap-unsaturated aldehyde selected from the group consisting of acrolein and methacrolein with oxygen in the vapor phase in the presence of water at a temperature in the range of about 400 F. to 850 F. and a catalyst comprising at least one member of the group consisting of the oxides of vanadium, the oxides of silver, and silver vanadate.

3. A process for the manufacture of an cap-unsaturated mono-carboxylic acid which comprises the step of reacting an a,fi-unsaturated aldehyde selected from the group consisting of acrolein and methacrolein with oxygen in the vapor phase in the presence of water and a catalyst comprising at least one member of the group consisting of the oxides of vanadium, the oxides of silver, and silver vanadate, said reaction being conducted at a temperature in the range of about 400 to 850 F. and at a contact time in the range of 15 to 25 seconds.

4. A process for the manufacture of acrylic acid which comprises the step of reacting acrolein with oxygen in the vapor phase at a temperature in the range of about 400 F. to 850 F. and in the presence of a catalyst comprising at least one member of a group consisting of the oxides of vanadium, the oxides of silver, and silver vanadate.

5. The process of claim 4 in which water is added to the reaction mixture.

6. The process of claim 4 in which the catalyst comprises silver vanadate and silica gel.

7. A process for the manufacture of methacrylic acid which comprises the step of reacting methacrolein with oxygen in the vapor phase at a temperature in the range of about 400 F. to 850 F. and in the presence of a catalyst comprising at least one member of the group consisting of the oxides of vanadium, the oxides of silver, and silver vanadate.

8. The process of claim 7 in which water is added to the reaction mixture.

9. The process of claim 7 in which the catalyst comprises silver vanadate and silica gel.

References Cited in the file of this patent UNITED STATES PATENTS 2,462,938 Bludworth et a1 Mar. 1, 1949 FOREIGN PATENTS 369,963 Great Britain Mar. 17, 1932 541,930 Great Britain Dec. 18, 1941 

1. A PROCESS FOR THE MANUFACTURE OF AN A,B-UNSATURATED MONO-CARBOXYLIC ACID WHICH COMPRISES THE STEP OF REACTING AN A,B-UNSATURATED ALDEHYDE SELECTED FROM THE GROUP CONSISTING OF ACROLEIN AND METHACROLEIN WITH OXYGEN IN THE VAPOR PHASE AT A TEMPERATURE IN THE RANGE FROM ABOUT 400*F. TO 850*F. AND IN THE PRESENCE OF A CATALYST COMPRISING AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF THE OXIDES OF VANADIUM, THE OXIDES OF SILVER, AND SILVER VANADATE. 